I want to install a new dual spotlight fitting in my bathroom but am a bit confused about wiring . At present i have a rose fitting with the following wiring set-up, 2 grey cables coming out of ceiling , each grey cable has 1 blue, 1 red, 1 earth, and 1 yellow wire. ceiling rose connection are, 2 reds are the loop, 2 blues are the neutral, the 2 yellow wires are connected into the same terminal block next to the live wire coming from the pendant light, the neutral wire from the pendant light is in next to the other neutrals, none of the wires has a sleeve on it to indicate which is the switched live. the new light i want to put up has as follows: a terminal block with 4 connections. the 2 blue neutrals are in one, the 2 brown live are in another and the earth is in another one, which leaves 1 empty connention, so how do i wire up to new light fitting, can i also add that the pull cord light switch also operates the extractor fan which has a delayed timer.

Two important points to make first, 1.with regard to bathroom electrics you must check out the part "P" section of the building regs in relation to electrics as there are strict rules now governing what you can and cannot do. 2.The existing three core and earth cable you have which can be found in two way lighting circuits is now outdated with regard to new installations therefore red is now brown, blue is now black and yellow is now grey.

However with regard to your main question regarding wiring up the new light you want to install, now I can only go on what you have said about the existing installation, you say the live wire from your pendant lamp goes to the terminal containing yellow wires, therefore it is fair say(but never assume) one of these wires goes to the light switch to pick up the live when switched on (hence switch wire) therefore both yellow wires will be live and it is fair to say that the other one will go to the fan. So when you switch on the light the live goes to bulb and fan making them come on together.

So it is reasonable to say(but again never assume) that the two brown wires of your new fitting go to the existing yellow wires and the blue wires go to the existing neutral terminal.

To prove the point switch off power to these circuits and undo light switch to check colours and check colour of wiring going to fan.

However like I say never make assumptions when dealing with electrics and check out those part "P" regulations

There is no requirement to notify under approved document part p a replacement light fitting in a bathroom, if the circuit was extended/altered and additional lighting installed that would be different.

Also there is no requirement that old colours be updated to new versions of BS7671.

The core should be identified though.

What you have is a sep up were the fan is connected neutral, permanently live and switch live at ceiling rose.The yellow cores are switch live and terminated at live side of fitting, generally shared with the brown flex of the lamp. These yellows should have been sleeved or marked red.The two reds are permanently live and terminated at the live loop, this will be the spare on your connection block.The two blues are neutrals, terminated at neutral terminal with the blue flex of lamp.And earth cables yellow and green, connected together at earth terminal.